Bacteria, viruses, and other pathogens in water and food can cause
diarrhea, stomach ache, fever, and death. These pathogens are too
small to be seen, but can be detected with appropriate testing. Many
of these pathogens are present in human and animal feces and can pass
into water.

Solar disinfection, which relies on the ultraviolet (UVA) component
of daylight, will inactivate bacteria, viruses, and some cysts. It
has been proven effective against cholera, typhoid, dysentery,
crytosporidium, giardia, many forms of diarrheal disease, and polio.

How to Use Solar Disinfection

The following are basic points of solar disinfection. They must be
elaborated and adapted to local conditions.

1. Place water in clean plastic (PET or PETE plastic) or glass
bottles with labels removed. Bottles should have a top and be clear
but may have a slight bluish cast. Mineral water bottles are commonly
used. The bottles should be one to two liters. Larger bottles have
too much water for the light to penetrate.

2. Do not use water which is too turbid or cloudy. Large dark print
placed next to or under the bottle should be legible when viewed
through the bottle of water. If excessive turbidity is present, allow
it to settle in a separate container and then pour the clear water
off the top into a bottle. If this does not remove excessive
turbidity, prefilter the water through clean sand or several layers
of cloth.

3. Aerate the water to enhance disinfection by leaving about one inch
of air at the top of the bottle, securing the cap, and then shaking
the bottle for about 15 seconds. The air renders the bacteria and
viruses more water soluble and thus more easily disinfected by the
ultraviolet light.

4. It is best if the bottles are inclined to receive the most
sunlight. A common method is to place them on a corrugated roof or a
piece of corrugated roofing material away from animals. In warm
climates it is beneficial to place the bottles on a blackened surface
to warm them to 50 degrees Celsius in order to hasten the
disinfection process. When this temperature cannot be reached, the
bottles can be placed on a reflective surface to increase the
efficiency of the disinfection process.

5. Expose the bottles for four to five hours in full mid-day sun or
for a full day in cloudy weather. They should not be in the shade.
Many people find it convenient to place a set of bottles outside for
a full day for use the following day. After proper exposure, the
bacteria and viruses in the water will be disinfected and safe to drink.

6. Replace scratched, damaged, or cloudy bottles with new bottles. A
program for the distribution of new bottles and recycling of old
bottles should be developed, especially if plastic bottles are used.

7. Where bottles are not available, water can be placed in clear
plastic bags, shallow pans, or shallow "plastic puddles"
made with plastic sheets or tarpaulins. If possible, water in pans or
"plastic puddles" should be covered with clear plastic
sheeting to protect it from bird droppings, insects, and other contamination.

8. Do not burn plastic. Burning plastic can be highly toxic.

Advantages and Limitations of Solar Disinfection

Solar disinfection is a simple, low cost method for disinfecting
small quantities of drinking water. By relying on the ultraviolet
(UVA) in daylight to disinfect bacteria, viruses, and other pathogens
in the water, it does not require any chemicals and does not change
the color or taste of water.

Solar disinfection does not require the availability or purchase of
chemicals or equipment and is thus immediately accessible to millions
of people throughout the world. It is appropriate and highly
effective for use in emergencies and disasters and on an on-going
basis in daily life where clean water is not available.

By helping reduce the incidence of diarrheal diseases, the use of
solar disinfection can reduce human suffering, the economic cost of
disease, and the additional burden on women of caring for sick
children. Since it reduces the need for fuel and firewood, it has
beneficial environmental effects.

Although solar disinfection disinfects bacteria and viruses, its
effect on some cysts and worms has not been fully researched and
should not be assumed. It does not remove pesticides or chemical
contaminants. It cannot be used with very turbid or cloudy water.

Drinking water purified by solar disinfection during one part of the
day does not protect against consumption of contaminated drinking
water at other times. While promoting health, clean water should not
be considered to be a "medicine".

Use of solar disinfection should be combined with good hygiene such
as washing hands after using the toilet, after cleaning a baby, after
handling animals and before eating in order to reduce the incidence
of disease.

For further information about GRI's Sun Water program, to offer
suggestions, to discuss ways of partnering with us, and to engage in
a dialogue regarding solar disinfection, please contact Peter
Moulton, Ph.D., Executive Director at <pmoulton@grilink.org>